To facilitate an understanding of the present invention the following terms will be used with the meanings set forth in the text that follows.
As used herein the term “mass spectrometry” refers to analytical techniques that measure the mass to charge ratio of ions. For the purpose of this discussion, unless otherwise indicated, the term includes time of flight, sector quadrupole, ion trap, Fourier transform ion cyclotron resonance, and tandem mass spectrometers.
Mass spectrometers receiving liquid samples, for example, mass spectrometers coupled to liquid chromatographic systems, have commonly used a device known as atmospheric pressure ionization to atomize liquid samples and place charges on the droplets and molecules. One normally does not wish to know the mass to charge ratio of droplets but rather one or more molecules contained in the droplets. As used herein, molecules for which information regarding mass to charge ratios is desired are referred to as analytes. Atmospheric pressure ionization may comprise the steps of electrospray, atmospheric pressure chemical ionization, or photoionization.
Droplets are desolvated to leave analyte molecules and other molecules carried in the sample. As the droplets are desolvated, molecules with charges, ions, remain. These ions enter a small opening often having a cone-like covering, into vacuum regions of the instrument. The atmospheric pressure ionization device is normally contained in an atmospheric pressure ionization housing at or near atmospheric pressure and prevents the sample from being discharged into the laboratory in which the mass spectrometer is placed.
The atmospheric pressure ionization housing is typically equipped with ports for introducing inert gases to facilitate solvent removal. Atmospheric pressure ionization housings are often equipped with a corona discharge pin for effecting atmospheric pressure chemical ionization. A corona discharge pin or needle is used to discharge electrons which electrons may cause molecules and droplets to form charged droplets and ions. Commonly, but not exclusively these electrons ionize reagent gases of solvent vapors, which ions then transfer their charge to analyte molecules.
As used herein, the term “vacuum regions” refers to those internal chambers of the mass spectrometer which are maintained at pressures below atmospheric pressure.
As used herein, the term “chromatography” refers to methods of separating compounds from each other by the different affinity such compounds will exhibit to different materials or phases. Gas chromatography refers to chromatographic separations in which the analyte is in a solution of gas. Gas chromatography mass spectrometry refers to the use of the outflow of a gas chromatographic system as the inlet source of a mass spectrometer. Gas chromatographic systems interfaces with mass spectrometers do not usually need to desolvate the sample because the sample is a gas, not a liquid. The gas chromatographic system can place the end of the column in substantially direct fluid communication with a source of electrons and the inlet of the mass spectrometer.
Liquid chromatography mass spectrometry refers to the use of a liquid chromatographic system coupled to a mass spectrometer. Liquid chromatographic systems are typically coupled to a mass spectrometer by means of an atmospheric pressure ionization and atmospheric pressure ionization housing. The atmospheric pressure ionization housing are sized and shaped to effect desolvation and commonly receive a liquid sample.
Gas samples received in an atmospheric pressure ionization housing are overly diluted and do not respond well to changes in sample composition. The separation effected by gas chromatographic processes are lost or lose definition.
However, due to the large capital cost of mass spectrometers, it is desirable to have the mass spectrometer capable of receiving and processing a broad range of samples, both liquid and gas samples, in a manner that is accurate and reproducible.